High frequency modulation cathode ray tube



g- 9, 1969 D. KETCHPEL HIGH FREQUENCY MODULATION CATHODE RAY TUBE 2 Sheets-Sheet 1 Filed Oct. 26, 1967 M, .2 M #p wm v a 4 M R. D. KETCHPEL 3,462,542

HIGH FREQUENCY MODULATION CATHODE RAY TUBE Aug. 19, 1969 Filed Oct. 26, 1967 2 Sheets-Sheet 2 United States Patent 3,462,642 HIGH FREQUENCY MODULATION CATHODE RAY TUBE Richard D. Ketchpel, Malibu, Califi, assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware .Filed Oct. 26, 1967, Ser. No. 678,294

. Int. Cl. H015 29/52 US. Cl. 31530 8 Claims ABSTRACT OF THE DISCLOSURE A cathode ray tube is provided having a conventional cathode with a cathode control grid positioned immediately forwardly thereof. Coaxial leads to the cathode and grid to provide electrical bias are provided and comprise coaxial cavities formed peripherally in the tube and extending transversely of the tube axis. The cavities include a central pin extending through both cavities transversely of the tube and a sleeve telescopically mounted to the external aspect of one cavity. Wire leads connect the pin and the sleeve to the grid and cathode, respectively. The coaxial line terminates in an external resistance refleeting the characteristic impedance of the line.

The invention relates to a broad-band frequency modulation cathode ray tube having particular utility in radar devices and the like.

There has been an increasing demand for cathode ray tubes the electron beam of which may be modulated at extremely high rates. For example, in high efficiency radar arrangements it is frequently desirable to provide cathode ray resolution which effectively responds to radar signals having an effective real time measuring characteristic in the fraction of a nanosecond range. Additionally, it is desirable to provide a cathode ray tube that will respond not only to these extremely rapid signals but can effectively respond to signals over a wide frequency range thereof, for example, from direct current input grid bias up to 500 megacycles.

Prior art arrangements in attempting to provide this wide-band and rapid response have generally been ineffective. One such example utilized a conventional control grid positioned forwardly of the cathode of a conventional cathode ray tube and interposed therebetween a modulating grid to provide a beam modulating signal to the grid via a coaxial conductor which entered the tube at the rear aspect thereof adjacent the conventional pin connectors. The inner cylinder of the coaxial line was connected to the cathode. This prior art design suggested that the modulating grid potential be held constant and that the cathode potential be varied to provide the' on time and cutoff of the electron beam. Additionally, a third grid cup was provided surrounding the main grid to provide the DC. bias necessary for electron beam cutoff. Heaters for the cathode were supplied with decoupling inductors so that the heaters could be periodically isolated from ground during the high frequency signal input so that the driving signal on the cathode would not be short-circuited. It has been found that structures involving this arrangement were inherently severely limited and wide-band modulation including high frequency modulation response was not satisfactorily achieved.

Other arrangements employed similar structure, that is, the feeding of both the cathode and a modulating grid via a coaxial conductor entering from the rear aspect of the cathode ray tube but dififered slightly from the structure described above. Again, the inner conductor was electrically connected to the cathode while the outer conductor was joined to a beam modulating grid placed 3,462,642 Patented Aug. 19, 1969 ice immediately adjacent the cathode. An arrangement of pin connections were provided to electrically bias the heaters. Utilizing this arrangement, it was found that the coaxial line did not terminate in its characteristic impedance, in effect creating an open circuit condition at the line terminus resulting in repeated energy impulse reflections back through the coaxial line until the energy wave was finally absorbed by the generator impedance. This open circuit condition, therefore, effectively prevented beam modulation over a wide band and particularly in the high frequency range, for example, 500 megacycles.

Accordingly, it is a primary object of the invention to provide a cathode ray tube structurally arranged to pro vide wide band beam modulation and beam modulation at high frequency, for example, up to 500 megacycles.

It is a further object of the invention to provide a cathode ray tube arrangement of the type described having a functional characteristic noted with a unique coaxial feed structural arrangement.

It is a specific object of the invention to provide a cathode ray tube of the type described employing a single modulating grid in combination with a coaxial feed extending generally transversely of the axis of the gun and structurally arranged to avoid open circuit termination condition on the coaxial feed and to balance capacitance and inductive impedance effects to thereby achieve the functional characteristics desired.

It is a further object of the invention to provide a cathode ray tube of the type described having coaxial feed extending generally transversely of the axis which allows coupling to the control grid in close proximity thereto as compared with coaxial feeds communicating with the tube at the rear aspect thereof.

It is a further object of the arrangement to provide a cathode ray tube in which the transverse coaxial feed accommodates coaxial line termination in a resistance device employing the characteristic impedance of the line thereby eliminating the disadvantageous pulse reflections described above. In addition, the terminating resistor may be positioned externally of the tube whereby the heat re sulting from power dissipation may be easily discharged to ambient and the resistance arrangement may be easily reached in the event repair is required.

It is a further specific object of the invention to provide a cathode ray tube of the type described having the functional characteristics noted wherein beam modulation is accomplished by grid drive with the cathode being biased to a fixed level thereby avoiding decoupling problems in re the heater connections noted above.

It is yet a further object of the invention to provide a cathode ray tube of the type described and having the functional characteristics noted wherein DC bias to the gun does not require an additional grid.

It is yet another object of the invention to provide a cathode ray tube of the type described having physical characteristics lending to ease of tube assembly and disassembly for repair.

These and other objects of the invention will become apparent in the course of the following description and from an examination of the related drawings wherein:

FIGURE 1 is a fragmentary, vertical, sectional view, partially in elevation, illustrating a presently preferred embodiment of the tube;

FIG. 2 is a fragmentary, partially elevational, detailed view of the external structure at the gun end of the tube; and

FIG. 3 is an end-elevational view taken from the right of the structure shown in FIG. 2.

Describing the invention in detail and directing attention to FIG. 1, the numeral 10 indicates generally a cathode ray tube having the wide band rapid frequency modulation characteristics described above. It is noted that 7 FIG. 1 is fragmentary illustrating only the gun'structu're of the cathode ray tube which incorporates the hereindisclosed invention. The balance of the structural features of the cathode ray tube such as the tube face, focus and deflection coils, power supplies, and the like, are conventional and well known in the art and, accordingly, not herein shown.

The electron gun structure is indicated generally at 12 and is enclosed in an annular evacuated small diameter tube section indicated generally at 14. The tube section 14 may be of any conventional construction and is not necessarily limited to the one herein described. However, the structure disclosed is an accurate representation of the tube employing the un structure which was actually constructed and operated and is presently preferred.

The tube 10, therefore, comprises a soft glass forward segment 16 having annular copper segment 18 sealed to the soft glass segment as at 20 and extending rearwardly to an annular Kovar segment 22, the juncture being between the Kovar segment 22 and the copper segment 18 being provided by a brazed joint at 24. A second Kovar segment 23 is joined to segment 22 as at 25. At the rear of the Kovar segment 22 a hard glass end plate 26 is sealed to the former as at 28 to provide for tube closure. A plurality of conventional electrical connections are indicated generally at 30 and are mounted to the glass plate 26 in the conventional manner. The electrical connections or stems 30 provide a means to electrically bias the various internal parts of the gun as will be well known to those skilled in the art. For example, stem 32 may be electrically connected to an anode 34 via wire lead 36 whereas stem 38 may be electrically connected to a cathode 40 via wire lead 42. Similarly, stem 44 may be connected via wire lead 46 and supporting structure 48 to the gun heater 50. The cathode 40 and heater 50 are supported by ceramic plate 52, the latter being carried in position along the central axis 54 of the gun by glass multi-form structure 56 having supporting U-shaped elements 58. In addition to the structure described, modulating grid 60 is carried by the ceramic structure 52 and is provided with an aperture 62 immediately forward of the cathode 40 and axially aligned with an aperture 64 in the anode 34, said apertures providing openings for the emanating electron beam.

A coaxial input arrangement is indicated generally at 66 and comprises annular transverse cavities 68 and 70 in spaced relationship and having connection pins 72 and 74 formed therein. The connection pins 72 and 74 are unitary and extend across the axis 54 of the gun. The walls of cavities 68 and 70 may be formed of electrically conductive metal such as Kovar and are joined at their inner aspects by insulating glass or ceramic 76, 76. The pin 72 is connected via wire line 78 to the modulating grid 60 and the cavity 70 is provided with a depending electrically conductive tantalum foil cylinder 80 which extends inwardly toward the axis 54 of the gun. The cylinder 80 is electrically connected via line 82 to the cathode 40 as is shown. The significance of this structure and the relationship of the various parts will be hereinafter described in detail.

Directing attention to FIGS. 2 and 3, the rear aspect of the cathode ray tube 10 is here shown with external structure applied thereto. The hard glass plate is shown at 26 and the Kovar section 22 is positioned immediately forwardly thereof. A linearly elongated Mylar sheet is shown at 90 and is peripherally wrapped around the cylindrical segment of the tube in the area of the transverse coax feed 66. Pin 72 is also shown in fragmentary section. An annular metallic clamp 92 surrounds the next section of the gun and provides means to support connected coaxial cable 94 which is positioned for electric juncture within the socket 68 of FIG. 1. The electrically conductive Kovar segment 22 and the electrically conductive clamp 92 combine with the interposed dielectric 4. Mylar sheet to form a capacitor as will hereinafter be described in detail. A resistor arrangement 96 is carried by the clamp 92 and electrically disposed in socket 70 of FIG. 1 to provide for the termination of a coaxial line with its characteristic impedance. The outer walls 70 and 68 and the cylinder are electrically interconnected by lead 100.

In view of the fact that lead 78 and lead 82 connect to the modulating grid 60 and cathode 40, respectively, and extend generally parallel as individual conductors within the spatial aspects of the tube, it has been found that distances A and B as shown in the drawing must be empirically arranged to balance inductive and capacitive elfects in the lines 78 and 82. With appropriate distances A and B, the effects cancel each other out and no undesirable attributes result. For example, in providing a cathode ray tube to modulate broadly from the DC. bias input to the grid 69 up to 500 megacycles, it was found that an A dimension of A1" and a B dimension of 4 produced the effect desired. The cylindrical skirt 80 connected to the coax cable 70 facilitates variation of this dimension because it may be telescopically moved up and down over the surface of the coax connection 70. A simple test has been evolved to provide accurate control of the A and B dimension for a given tube design. All that is required is that a conventional reflectometer be connected to the coax leads and the distances A and B varied relative to each other until reflection in the line is at an absolute minimum. As an aid to making the adjustments, as above described, the joint 25 may be left unwelded until adjustment of dimensions A and B are complete. Upon achieving satisfactory operation joint 25 may be electron beam welded to complete the structure. Tubulation may be conventionally provided as at 71 to accommodate evacuation setting up the required vacuum condition in the tube 10.

The above-described arrangement when actually constructed provides a mode of terminating the coaxial lead with a resisting device effectively equaling the characteristic impedance of the line and thereby preventing the inline reflection characteristic of prior art devices. Additionally, the balanced position of the leads 78 and 82 mutually cancelling out capacitance and inductive effects enabled the tube as disclosed to eifectively modulate the electron beam through a range from the DC. drive input upwardly of 500 megacycles. As a result of this efficient modulation, the resolution of the displayed image was substantially improved effecting an important improvement in the reading and recording of radar signals having a real time existence in the fraction of a nanosec- 0nd. The design, therefore, represents a substantial improvement in the structure and operative features of cathode ray tubes as compared with prior art devices. It will also be noted that the elimination of protruding structure from the periphery of tube section 14 accommodates the easy assembly of deflecting coils and other cathode ray tube structure.

The invention as shown is by way of illustration and not limitation and may be modified in many respects all within the scope of the appended claims.

What is claimed is:

1. In a cathode ray tube structure providing electron beam modulation, the combination of,

a cathode structure disposed generally axially of the tube,

a cathode control grid positioned forwardly of and coaxial line connection means for coaxial line conimmediately adjacent the cathode structure,

coaxial line connection means for coaxial line connection formed in the tube and extending generally transversely of the tube axis,

said connection means including leads internally of the tube to provide electrical connection to the cathode structure and the control grid, respectively, and a resistance device associated with the connection means and accessible to the external aspect of the tube providing for termination of the coaxial line in the characteristic impedance of the line. 2. A cathode ray tube structure providing electron beam modulation according to claim 1,

wherein one of said leads internally of the tube joins the inner aspect of the coaxial line to the control grid, another of said leads internally of the tube joining the outer aspect of the coaxial line to the cathode structure. 3. A cathode ray tube structure offering modulation according to claim 2,

wherein said leads are positioned relative to each other to balance inductive and capacitive effects in said leads relative to each other. 4. A cathode ray tube structure providing electron beam modulation according to claim 3, wherein said connection means comprises socke formed in the wall of the tube and extending transversely of the tube axis, and means to physically vary the position of the leads relative to each other comprising a skirt connected to one of said leads and to one socket and movable relative to the latter. 5. A cathode ray tube structure providing electron beam modulation according to claim 4,

wherein the sockets include a central pin extending transversely of the tube and into both sockets and electrical connection means connecting the peripheral portion of said sockets. 6. A cathode ray tube structure providing electron beam modulation according to claim 5, and including,

other electrical connection means protruding from the rear aspect of the tube and generally parallel to the tube axis. 7. In a cathode ray tube structure providing electron beam modulation, the combination of,

a cathode structure positioned generally axially of the tube,

a cathode control grid mounted forwardly of and immediately adjacent the cathode structure,

first electrical connection means comprising pins protruding from the rear axis of the tube and extending generally parallel to the tube axis,

second coaxial line connection means for coaxial line connection mounted on the tube peripherally thereof and extending generally transversely of the tube axis,

said second connection means comprising a center pin extending through and transversely of the axis of the tube and into opposed sockets,

the outer aspects of the sockets being electrically joined internally of the tube,

and line means interconnecting the center pin and the control grid and the outer aspects of the sockets and the cathode, respectively,

said line means being positioned to balance the inductive and capacitive etfects therein.

8. A cathode ray tube structure providing electron beam modulation according to claim 7, and including,

resistance means mounted in one of said sockets and extending externally of the tube,

said resistance means terminating the related coaxial line in its characteristic impedance.

References Cited UNITED STATES PATENTS 2,128,639 8/1938 Diels 313-87 X 2,466,7 l1 4/ 1949 Kenyon 315--3 0 X 2,468,440 4/1949 Harries 313-87 X 3,360,678 12/ 1967 Kerns 315-3 RODNEY D. BENNETT, 111., Primary Examiner HERBERT C. WAMSLEY, Assistant Examiner U.S. Cl. X.R.

2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa n 3,462,642 Dated August 19 1969 Inventor(s) Richard Ketchpel It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4, line 67, delete "coaxial line connection means for coaxial line con-".

SIGNED AN'L- SEMFD DEC 2 3 1959 Attest:

mmamnemhuk' WILLIAM E. eoaumm, Attesting Officer Oomissioner of Paten 

